Implement loader interface and waiting on process

[roblabla]

• Loader now has an interface to spawn new processes at runtime.
• We can also add Loader to wait until a process is killed.

[todo]

Use a better lock around thread_maternity.

Thread maternity currently uses a SpinLock. We should ideally use a scheduling mutex there.

---

SunriseOS/kernel/src/process.rs

Lines 69 to 79 in 898433c

	// TODO: Use a better lock around thread_maternity.
	// BODY: Thread maternity currently uses a SpinLock. We should ideally use a
	// BODY: scheduling mutex there.
	thread_maternity: Vec<Arc<ThreadStruct>>,
	}
	impl ProcessStateData {
	/// Sets the state to the given new state, and signal the process, causing
	/// any threads waiting on the process to get woken up.
	fn set_state(&mut self, newstate: ProcessState) {
	self.state = newstate;

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This comment was generated by todo based on a TODO comment in 898433c in #488. cc @roblabla.

[todo]

Unify Handle/HandleRef behind a single trait.

The fact I have to do this makes me think there's really a problem in the handle/handleref design. Maybe there should be a trait unifying Handle/HandleRef, and `Process` and co should be generic on those? That would allow me to call the functions on "borrowed lifetime-erased" handles.
This trait could probably be AsRef or Borrow. Ideally the generic types would be an internal implementation details and we'd just expose "Process" and "ProcessBorrowed" types through typedef/newtypes. Needs a lot of thought.

---

SunriseOS/loader/src/main.rs

Lines 220 to 230 in 898433c

	// TODO: Unify Handle/HandleRef behind a single trait.
	// BODY: The fact I have to do this makes me think there's really a
	// BODY: problem in the handle/handleref design. Maybe there should be a
	// BODY: trait unifying Handle/HandleRef, and `Process` and co should be
	// BODY: generic on those? That would allow me to call the functions on
	// BODY: "borrowed lifetime-erased" handles.
	// BODY:
	// BODY: This trait could probably be AsRef or Borrow. Ideally the
	// BODY: generic types would be an internal implementation details
	// BODY: and we'd just expose "Process" and "ProcessBorrowed" types
	// BODY: through typedef/newtypes. Needs a lot of thought.

---

This comment was generated by todo based on a TODO comment in 898433c in #488. cc @roblabla.

[todo]

Return exit state.

SunriseOS/loader/src/main.rs

Lines 241 to 251 in 898433c

	// TODO: Return exit state.
	return Ok(0);
	}
	}
	}))
	}
	}
	fn main() {
	let fs = &*BOOT_FROM_FS;

---

This comment was generated by todo based on a TODO comment in 898433c in #488. cc @roblabla.

[marysaka]

lgtm